I have been searching for good resources about visualizing reliability and validity in research methodology, but could not find unlicensed or free (as beer and as speech) examples fitting my needs.

Well, my needs might seem specific, as I do not like the classic example of validity and reliability showed in most basic statistics/research methodology book (like Babbie’s The practice of social research) with the target and shots, as I assume, that thinking in 2 dimensions for starters seems more difficult with these terms. Just for the example see:

http://www.socialresearchmethods.net/kb/relandval.php

I tried with LaTeX and TikZ to build my own graphs which I share here in hope of someone could use these in the future.

First, I was searching for 1D coordinate systems in LaTeX, and came up with the idea to show measurements on a timeline. This could be easily done with chronology found on CTAN:

I really like this example, as showing all the possible values of the temperature of water (below 0 Celsius degree it is considered as ice, above 100 Celsius degree, it is considered as steam), so validity and reliability can be judged easily. The source code of my slide and the result can be seen above, feel free to (re)use it! (Note: the scale parameter was given in the header of tikzpicture to fit in the slide, because I was lazy to rewrite the code from centimeters. Sorry for that!)